In this study, the cellular protective effects on HaCaT cells and human erythrocytes and antioxidative effects of P. tricuspidata stem extracts were investigated. The ethyl acetate (50 µ g/mL) and aglycone fraction (25 µ g/mL) of P. tricuspidata stem extracts doesn't show any characteristics of cytotoxicity. When HaCaT cells were treated with 10 mM H2O2 and 30 µ M rose bengal, the ethyl acetate (6.25 ∼ 50 µ g/mL) and aglycone (6.25 ∼ 25 µ g/mL) fraction protected the cells against the oxidative damage in a concentration dependent manner. The P. tricuspidata stem extracts showed more prominent cellular protective effect than (+)-α-tocopherol, known as lipid antioxidant at 10 µ g/mL. The ethylacetate fraction of P. tricuspidata stem extracts (18.5 µ g/mL) showed more free radical (1,1-diphenyl-2-picrylhydrazyl, DPPH) scavenging activity (FSC550). Reactive oxygen species (ROS) scavenging activity (OSC50) of P. tricuspidata stem extracts on ROS generated in Fe 3+ -EDTA/H2O2 system was investigated using the luminol-dependent chemiluminescence assay. The ethyl acetate (1.72 µ g/mL) and the aglycone fraction (1.53 µ g/mL) showed similar ROS scavenging activity of L-ascorbic acid (1.50 µ g/mL). These results indicate that extract/fractions of P. tricuspidata stem extracts can function as natural cytoprotective agents and antioxidants in biological systems, particularly skin exposed to UV radiation by protecting cellular membrane against ROS.